Methylchloroform is an outstanding solvent and finds wide application in cleaning and degreasing operations. Stabilizers are usually compounded with methychloroform to give solvent systems which are resistant to the degradation of methylchloroform into by-products such as hydrogen chloride and acetic acid. The tendency for such degradation is especially pronounced in the presence of metals or moisture.
Despite the initial resistance of stabilized methylchloroform systems to decomposition, it is usual for acidity to develop over long periods of continual use. Although solvent contaminants may be removed by processes such as filtration or redistillation, the stabilization capacity of the solvent systems (its ability to accept acids and render them harmless) is gradually diminished. The development of an acidic environment (e.g., such as results from the presence of free hydrochloric acid or acetic acid) is particularly detrimental to the cleaning of metals because it may result in corrosion or the appearance of etched surfaces.
U.S. Pat. No. 3,209,040 (patented Sept. 28, 1965) describes a process for treating trichloroethylene or perchloroethylene to remove oxidation products by intimate mixing with an aqueous solution of a polyol for a period of 15 to 60 minutes, then cooling followed by separation of an aqueous phase.
U.S. Pat. No. 3,360,474 (patented Dec. 26, 1967) and U.S. Pat. No. 3,452,110 (patented June 24, 1969) describe compositions of filtering powder, polyhydroxy alcohol, and an inorganic base for treatment of drycleaning fluids. This composition is maintained as a suspension in the drycleaning fluid for approximately 15 minutes and separated by filtration.
It is desirable to develop a process to continuously and conveniently maintain over long operating periods the pH and acid acceptance of methylchloroform solvent employed in cleaning and degreasing operations.